In the fabrication of integrated circuits, various conductive layers are used. For example, during the formation of semiconductor devices, such as dynamic random access memories (DRAMs), static random access memories (SRAMs), ferroelectric (FE) memories, etc., conductive materials are used in the formation of storage cell capacitors and also may be used in interconnection structures, e.g., conductive layers in contact holes, vias, etc. In many applications, it is preferable that the material used provide effective diffusion barrier characteristics. For example, diffusion barriers are commonly used to prevent undesirable reactions in contact openings.
Further, for example, effective diffusion barrier characteristics are required for conductive materials used in the formation of storage cell capacitors of memory devices, e.g., DRAMs. As memory devices become more dense, it is necessary to decrease the size of circuit components forming such devices. One way to retain storage capacity of storage cell capacitors of the memory devices and at the same time decrease the memory device size is to increase the dielectric constant of the dielectric layer of the storage cell capacitor. Therefore, high dielectric constant materials are used in such applications interposed between two electrodes. One or more layers of various conductive materials may be used as the electrode material. However, generally, one or more of the layers of the conductive materials used for the electrodes (particularly the lower electrode of a cell capacitor) must have cerain barrier properties and oxidation resistance properties. Such properties are particularly required when high dielectric constant materials are used for the dielectric layer of the storage cell capacitor because of the processes used for forming such high dielectric materials, e.g., deposition of high dielectric materials usually occurs at high temperatures (generally greater than about 500.degree. C.) in an oxygen-containing atmosphere.
Generally, various metals and metallic compounds, and typically notable metals such as platinum and conductive oxides such as ruthenium oxide, have been proposed as the electrodes or at least one of the layers of the electrodes for use with high dielectric constant materials. However, reliable electrical connections should generally be constructed which do not diminish the beneficial properties of the high dielectric constant materials. For platinum to function well as a bottom electrode, it must be an effective barrier to the diffusion of oxygen. This is required since any oxidation of underlying silicon upon which the capacitor is formed will result in a decreased series capacitance, thus degrading the storage capacity of the cell capacitor. Platinum, used alone as an electrode layer, is too permeable to oxygen to be used as a bottom electrode of a storage cell capacitor. For example, there should also be a silicon barrier so that silicon does not diffuse through the platinum to form SiO.sub.2 at the platinum surface.
Because of the permeability of platinum to oxygen, typically platinum is used as a layer in an electrode stack which acts as the electrode as well as a diffusion barrier for integration of capacitors directly formed on silicon. For example, as described in the article "Novel High Temperature Multilayer Electrode-Barrier Structure for High Density Ferroelectric Memories" by H. D. Bhatt, et al., Appl. Phys.Letter, 71(5), Aug. 4, 1997, the electrode barrier structure includes layers of platinum:rhodium alloy, in addition to platinum:rhodium oxide layers, to form electrodes with diffusion barrier properties. Such alloy layers are formed using physical vapor deposition (PVD) processing, e.g., reactive RF sputtering processes. Additionally, the formation of a platinum film was described by Kwon et al., wherein the deposition was accomplished by metallorganic chemical vapor deposition from hydrocarbon precursors in an oxygen atmosphere in the temperature range of 300.degree. C. to 450.degree. C. for various deposition times. "Characterization of Pt Thin Films Deposited by Metallorganic Vapor Deposition for Ferroelectric Bottom Electrodes," J. H. Kwon et al., J. Electrochem. Soc., Vol. 144, No. 8, pp. 2848-2854 (1997).
Many storage cell capacitors are formed using high aspect ratio openings. For example, in U.S. Pat. No. 5,392,189 to Fazan, et al., entitled "Capacitor Compatible with High Dielectric Constant Materials Having Two Independent Insulative Layers and the Method for Forming Same," issued Feb. 21, 1995, the storage cell capacitors include a lower electrode that is formed by deposition of a conductive material within a small high aspect ratio opening. Typically, sputtering does not provide a sufficiently conformal layer adequate for formation of an electrode within such a small high aspect ratio opening.
Chemical vapor deposition (hereinafter "CVD") is one process of forming relatively thin layers on semiconductor wafers, such as layers of elemental metals or compounds. It is a favored layer formation process primarily because of its ability to provide highly conformal layers even within deep contacts and other openings. CVD is defined as the formation of a non-volatile solid layer or film on a substrate by the reaction of vapor phase reactants that contain desired components. The vapors are introduced into a reactor vessel or chamber, and decompose and/or react at a heated surface on a wafer to form the desired layer.
For example, a compound, typically a heat decomposable volatile compound (also known as a precursor), is delivered to a substrate surface in the vapor phase. The precursor is contacted with a surface which has been heated to a temperature above the decomposition temperature of the precursor. A coating or layer forms on the surface. The layer generally contains a metal, metalloid, alloy, or mixtures thereof, depending upon the type of precursor and deposition conditions employed.
Precursors typically utilized in CVD of conductive layers are generally organometallic compounds, wherein a hydrocarbon portion of the precursor functions as the carrier for the metal or metalloid portion of the precursor during vaporization of the liquid precursor. For microelectronic applications, it is often desirable to deposit layers having high conductivity. This generally means that the layers should contain minimal contaminants, such a oxygen, carbon, and the like. In addition to the formation of capacitor electrodes, the formation of barrier layers for use in other applications, e.g., interconnect applications, is also desirable. For example, diffusion barriers are commonly used to prevent undesirable reactions in contact openings.